[Haskell-cafe] Re: Refactoring status

[Bob]

On 2008-01-04 0:23, Bulat Ziganshin wrote:
> Hello C.M.Brown,
> 
> Thursday, January 3, 2008, 10:46:54 PM, you wrote:
> 
>>> i don't use
>>> type signatures at all - this creates some problems when i wrote large
>>> portion of code and try to make it compile, but nothing more
> 
>> I believe type signatures are the very essence of Haskell documentation!
>> I'd much rather see a program with type signatures for functions and
>> little (or no) comments over programs with no type signatures and
>> ambigious comments (if any comments at all!).
> 
>> Type signatures really does make dealing with someone elses code that
>> much easier.
> 
> well, i don't worry about types of things with which i work. i know
> that it is a file, for example. its actual type depends on the
> information i need inside this function. it may start as FileInfo type,
> then after refactoring it will become CompressedFile or
> (fileInfo,FileSize) type. while it's great to know types of every
> variable to better understand how program works, adding type
> signatures means more work when writing program and when changing it.
> i want to express only data processing algorithm leaving all the
> details to compiler. for me, ghc just "reads thoughts"
> 
> types and type signatures was required in classic languages to fight
> with errors. but in haskell omitting type signatures doesn't make
> program less reliable, so i don't need to write this extra code in
> addition to the essential - algorithm itself. for the same reason, i
> like pointless notation
> 

You are wrong. Without type signatures some type errors will not be
caught by the compiler, resulting in erroneous program behaviour.
An example:

makeURI file index = "http://192.168.0.1/somescript.php?file=" ++
    urlEncode file ++ "&index=" ++ show index

the intended signature for the above function is:
String -> Int -> String, but suppose I've used it that way:
makeURI "somefile.txt" "1"
this is a type error, String was used where Int was expected,
but the program compiles just fine. So now the string:
http://192.168.0.1/somescript.php?file=somefile.txt&index="1"
will be sent to the server which is of course wrong because
http://192.168.0.1/somescript.php?file=somefile.txt&index=1
is expected.

Without type declarations You are not using the full power
of static type checking.